1. Field of the Invention
The present invention relates to a key sheet for pushbutton switches to be used in the operating portions of various portable electronic apparatuses such as a mobile phone, a personal digital assistant (PDA), and a notebook PC. In particular, the present invention relates to a key sheet having pushbuttons (key tops) to be depressed to effect input and a coordinate sensor for detecting the movement path of a finger when effecting input by stroking the surfaces of the pushbuttons with the finger.
2. Description of the Related Art
As components of the input operating portion of an electronic apparatus such as a mobile phone or a PDA, there are known a plurality of key tops to be depressed with a finger of the operator to effect input, and a coordinate sensor for detecting the movement path of the finger with which the operation surface formed by the top surfaces of the key tops is stroked to effect manual input. For example, JP 2002-196856 A discloses a key pad in which there are arranged a key mat provided with key tops convex on the front surface side and a capacitance sensing plate as a coordinate sensor provided on the back surface side of the key mat. Through depression of the key tops, this key pad allows depressing operation input like pushbutton switches; by stroking the operation surface formed by the top surfaces of a plurality of key tops with a finger, it is possible to effect sliding operation input like a touch pad.
In the coordinate sensor as disclosed in JP 2002-196856 A, the movement path of the finger is sensed from a change in capacitance at a coordinate position and converted to input data, making it possible to detect the coordinate position if sliding operation input is effected through an intermediation of a thin cover or thin key tops without directly touching the sensor. However, the requisite depression load at the time of depressing operation input is rather high, and hence it is rather hard for the click feel to be transmitted, resulting in a rather poor depression operability.